1. Field of the Invention
The present invention relates to an image display apparatus.
2. Description of the Related Art
An image display apparatus to reflect a laser beam with a scanning mirror and to display an image on a projection surface by raster scanning with a beam has been known (see, for example, Patent Literature 1: JP 2010-539525 W). That is, a laser scanning type projection display draws a scanning line in a horizontal direction by making a scanning mirror perform reciprocating oscillation to the right and left. At the same time, the laser scanning type projection display makes the scanning mirror perform reciprocating oscillation in a vertical direction for the number of scanning lines included in an image.
The laser scanning type image display apparatus is used, for example, in a vehicle. In an in-vehicle image display apparatus, a video is displayed through a windscreen or a combiner in front of a driver (see, for example, Patent Literature 2: JP 5-8661 A). Accordingly, an image luminous flux emitted from the image display apparatus and external light transmitted through the windscreen are overlaid (superimposed) and enter an eye of the driver. Thus, the driver is able to see video information and a situation in front of him/her simultaneously.
Since being small and portable, an image display apparatus is expected to be used in various kinds of environment. For example, usage in environment with various levels of brightness is expected. Thus, it is desired to make it possible to perform adjustment of a wide range of light adjustment level, specifically, adjustment at low luminance in detail.